Protein tyrosine phosphorylation-dephosphorylation plays a very important role in intracellular signal transduction system. In particular, protein tyrosine phosphorylation-dephosphorylation is involved in changes of cells such as responses to foreign stimuli, cell growth, differentiation and apoptosis, etc. Therefore, protein tyrosine kinase (PTK; Curr Pharm Des 13:2751-65, 2007; Curr Med Chem 14:2214-34, 2007) and protein tyrosine phosphatase (PTP) are important target proteins for the treatment of such diseases accompanying the change of cells as cancer, vascular disease, immune disease and nervous disease (Curr Cancer Drug Targets 6:519-532, 2006; Med Res Rev 27:553-73, 2007). Human has approximately 100 kinds of PTPs (Cell 117:699-711, 2004). 20 kinds of these PTPs have been confirmed to be related to disease so that they have been targets of the development of a novel drug. And the remaining 80 kinds of PTPs are presumed to be related to disease as well.
According to the previous reports, PTP levels vary from disease and cell conditions (Crit Rev Oncol/Hemat 52:9-17, 2004; Expert Opin Therapeutic Targets 10:157-177, 2006). However, since there is no tools to measure the level of PTP in cells or blood directly, indirect methods such as measuring intracellular mRNA level by RT-PCR or Western blotting using commercial PTP antibody against limited PTP proteins are being used to quantify PTP. However, quantifying mRNA cannot tell exact amount of PTP. Besides, mRNA measurement is not possible with blood or urine samples. In the case of Western blotting, precise quantification of PTP is still difficult because only 10 PTP antibodies have been known and sensitivity of these antibodies is not very good. Despite PTPs are highly potent as a biomarker, development of a method for diagnosis of disease using these excellent biomarkers is not advanced, yet.
Blood samples, among many biosamples, are excellent test samples for diagnosis of disease using a biomarker, because of easiness in sampling and diversity of materials included in blood. Blood circulates everywhere in human body, during which blood takes cells a bit from each and every part of the body. These cells are broken, so that proteins included in those cells are flowing into blood. So, blood contains such proteins, telling conditions of the body. However, the amounts of such blood proteins are very small, so the presence of blood protein itself is sometimes neglected. In the meantime, large amount of proteins such as albumin and immunoglobulin are included in blood, which make it difficult to analyze minute proteins derived from cell.
To measure those PTPs existing at femto or atto mole level in blood, the present inventors selected standard peptides of PTP active domain facilitating the analysis of 80 kinds of PTPs by using mass spectrometer. So, peptides collected with antibodies binding specifically to the standard peptides are quantified by SISCAPA (Stable Isotope Standards and Capture by Anti-peptide Antibodies) technique that is a method to quantify protein based on mass spectrometry (Mol Cell Proteomics 5:573-588, 2006); Proc Natl Acad Sci USA 100:6940-6945, 2003). As a result, several PTPs demonstrated different levels between normal individual and cancer patient. The present inventors further completed this invention by confirming that the method of the invention facilitating analysis by PTP panel constructed by using standard peptides and their antibodies can be effectively used for diagnosis of disease.